One of the greatest advances made in pathology has been the establishment of the fact that a great many of the morbid conditions from which the human race suffer are those due to causes arising entirely from within their own systems and in consequence of deficiencies of elimination or of perverted physiological processes which, in large degree, are themselves the result of errors and indiscretions in diet, in manner of life, in habits, etc. That these general facts have been recognized for centuries is perhaps a credit to the powers of observation of practitioners of past generations. Exact knowledge, however, has come only with exact laboratory methods of research and most painstaking study of the secretions and excretions, both under normal and morbid conditions. The subject of _auto-intoxication_ has been too commonly relegated to the domain of internal medicine, and has been supposed to be one in which the surgeon need take only passing interest. The _alkaloids_ are by no means the only poisonous products which the human body may produce and retain. That most important excrementitious material of all--_i. e._, _carbon dioxide_--could not be retained in the organism for more than a few moments without death as the inevitable consequence. The various _soluble ferments_ elaborated by certain glands may exert deleterious influence, both local and general; and in the saliva are also found products which are not ferments. The _biliary acids_ also, if they do not find free escape, may produce fatal poisoning. So also _leucin_, _tyrosin_, and all the excrementitious products which arise from insufficient liver activity, are capable of producing forms of intoxication--such, for example, as _eclampsia_, etc. The character of the solvent has much to do with toxicity. Thus aqueous extract of putrid matter is more poisonous than that of fecal matter, while alcoholic extract of fecal material is more toxic than that of putrid. All the alkaloids produced within the body are not poisonous. Some are found in the normal tissues, and they are, perhaps, only one of the results of the disassimilation of animal cells. Nor are all these poisons of bacterial origin, although many are formed only in the presence of microbes.